This application is based on patent application No. 9-190194 filed in Japan, the contents of which is hereby incorporated by reference.
This invention relates to a display characteristic measurement apparatus for a color display apparatus which picks up an image of a measurement pattern displayed on a color display apparatus such as a color CRT (Cathode Ray Tube) and measures a display characteristic such as a convergence based on this image signal.
Conventionally, there has been known a display characteristic measurement apparatus for measuring a display characteristic such as a convergence of a display apparatus such as a color CRT, a color LCD (Liquid Crystal Display) or a color PDP (Plasma Display Panel). This display characteristic measurement apparatus includes an image pickup unit for picking up an image of a specified measurement pattern color-displayed on a display apparatus to be measured while separating this image into images of the respective color components of R (red), G (green) and B (blue), an image processor for conducting a predetermined measurement after processing the images of the respective color components, and a display device for displaying the measurement result.
For example, as disclosed in Japanese Unexamined Patent Publication No. 8-307908, a convergence measurement apparatus picks up an image of a specified white measurement pattern displayed on a color CRT to be measured by a camera provided with a color area sensor such as CCDs, calculates a luminance center for every picked image of each color component R, G or B during the image processing, and displays a relative displacement of these luminance centers as a misconvergence amount.
The convergence measurement apparatus calculates a luminous position (luminous center position) of the measurement pattern of each color component on a display surface of the color CRT to be measured based on a focusing position (luminance center position) of the measurement pattern of each color component on a sensing surface of the color camera, and calculates a relative displacement of the luminous positions of the respective color components. Accordingly, the accuracy of the convergence measurement is largely affected by the calculation accuracy of the focusing position (luminance center position) of the measurement pattern of each color component on the sensing surface.
Particularly in the case that a color camera of three-plate type is used, a light image is separated into images of three primary color components, and three area sensors are independently provided so as to conform to the respective color components of R, G, B at the respective emergence ends of a dichroic prism for emitting the images of the respective color components in different directions. Accordingly, the measurement accuracy easily varies due to displacements of the respective area sensors caused by temperature and humidity variations.
Accordingly, the conventional convergence i measurement apparatus is calibrated using a special calibration chart before a measurement as shown in FIG. 9. A calibration method shown in FIG. 9 is such that an image of a calibration chart 103 (a chart in which a crosshatched pattern 105 is drawn on an opaque white plate) illuminated by a fluorescent lamp 104 is picked up by an image pickup unit 101 of the convergence measurement apparatus 100 and a calibration data representing a relative positional relationship of the respective area sensors is calculated using the picked image. The calculated calibration data is stored in a memory in an apparatus main body 102 and used as a data for calibrating a displacement of the luminance center position of the measurement pattern of each color component during the convergence measurement.
According to the conventional method for calibrating the relative displacement of the area sensors, the positions (absolute positions) of the respective area sensors in reference coordinate systems in a convergence measuring system are calculated using the image data of the respective color components obtained by picking up the image of the special calibration chart, and the relative displacement of the area sensors is calculated based on this calculation result. Thus, there is a disadvantage of many operation parameters which necessitates a longer operation time.
Further, since not the measurement pattern displayed on the CRT to be measured, but the special calibration chart is used, it is inconvenient and difficult to calibrate convergence measuring systems at a production line.
It is an object of the present invention to provide a display characteristic measurement apparatus which has overcome the problems residing in the prior art.
It is another object of the present invention to provide a method for calibrating a display characteristic measurement apparatus which has overcome the problems residing in the prior art.
According to an aspect of the present invention, a display characteristic measurement apparatus for a color display apparatus, comprises: a first image pickup device which picks up an image of a first color component; a second image pickup device which picks up an image of a second color component; a measurement image generator which causes a color display apparatus to display a measurement image thereon, the measurement image being displayed in a single color to which both the first image pickup device and the second image pickup device are sensible; and a calculator which calculates, based on a first picked-up image picked up by the first image pickup device and a second picked-up image picked up by the second image pickup device, calibration data for calibrating a relative displacement between the first image pickup device and the second image pickup device.
According to another aspect of the present invention, a display characteristic measurement apparatus for a color display apparatus, comprises: a first image pickup device which picks up an image of a first color component; a second image pickup device which picks up an image of a second color component; a measurement image generator which causes a color display apparatus to display a measurement image thereon, the measurement image being displayed in a single color to which both the first image pickup device and the second image pickup device are sensible; a first position calculator which calculates, based on a first picked-up image picked up by the first image pickup device, a position on the first image pickup device that corresponds to a specified position of the measurement image on the color display apparatus; a second position calculator which calculates, based on a second picked-up image picked up by the second image pickup device, a position on the second image pickup device that corresponds to the specified position of the measurement image on the color display apparatus; and a displacement calculator which calculates, based on first and second positions calculated by the first and second position calculators, a relative displacement between the first image pickup device and the second image pickup device.
According to another aspect of the present invention, a method for calibrating a relative displacement between a first image pickup device for picking up an image of a first color component and a second image pickup device for picking up an image of a second color component provided in a display characteristic measurement apparatus for a color display apparatus, comprises the steps: causing a color display apparatus to display a measurement image thereon, the measurement image being displayed in a single color to which both the first image pickup device and the second image pickup device are sensible; picking up images of the measurement image displayed on the color display apparatus by the first and second image pickup devices, respectively; calculating, based on picked-up images of the first and second image pickup devices, calibration data for calibrating a relative displacement between the first image pickup device and the second image pickup device.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.